The purpose of the study is to examine the effects of breast-feeding on heart rate and blood pressure variability in mothers. Recent studies indicate that breast-feeding decreases stress levels and stress response in mothers. This decrease may be because breast-feeding changes sympathetic and parasympathetic nervous system which can be measured by heart period variability and blood pressure variability. Therefore, it will be instructive to see what effect breast-feeding has on these measures. It is hypothesized that breast-feeding will increase parasympathetic control (increase heart rate and blood pressure variability), and will decrease self-reports of stress. Women who both breast-feed and bottle-feed an infant will be asked to come in for two sessions. In one session, women will breast-feed their infant while non-invasively instrumented for heart rate and blood pressure measures. In the other session, women will bottle-feed their infant with the same instrumentation. In addition, self-report questionnaires of mood will be completed.